Perospero confirmed poison would work on her. It's been shown and said multiple times in the series that "internal" damage like poison, cold, and destroying organs are more effective than things like trying to stab, punch, or slice the "outer" body.
Because he doesn't know everything and most people would assume that poison would kill another person but we don't know that it could. I'm not saying the poison absolutely wouldn't work but that we don't know if it would similar to how Luffy has an unnatural high resistance to poison or like how Reiju has an ability to control poisons, maybe BM also has some means to prevent poisons(or most poisons) from working.
Well in fact he has shown why he is a Yonko. He literally stopped 2 big fights just with his presence. ¿Emperor Haki?
Poison doesn't work on luffy. Sure he fought Magellan, but big mom can't fight Magellan? Lmao luffy tankes Caesars strongest poison, the same they tried to kill big mom with. Lmao Prospero even said the poison could not work. Big mom isn't gonna be hurt by poison lmao
Poison doesn't work on Luffy because Iva's power strengthened his immune system towards it, and we've seen that that immunity isn't even immunity, but resistance. You can't really go "Luffy can tank Caesar's poison, but BM can't?" when Luffy tanking Caesar's poison had nothing to do with him being strong, but a very particular event happening to strengthen his immune system.
Vega punk could probably make poison strong enough he’s being held captive by the government because he’s that smart
